The present invention relates to respirators in general and, in particular, to a new and useful respirator construction, particularly adapted for use with infants for providing a plurality of respiration cycles including the intermittent positive pressure ventilation cycle (IPPV), the positive end expiratory pressure (PEEP), the continuous positive airway pressure (CPAP) and the intermittent mandatory ventilation (IMV).
In order to obtain optimum therapeutic results when using respirator devices, it is necessary to design such respirators so that they can be adapted to different methods or cycles of operation which are proper for several respective physiological requirements.
Vitally nourished premature and newborn babies require first intermittent positive pressure ventilation (IPPV), which are combined primarily with an positive end-expiratory pressure (PEEP). After a recovery phase of the thorax muscles and beginning normalization of the blood gas values, respiratory gas with the necessary oxygen concentration can be given in spontaneous respiration, if necessary, under a continuously positive airway pressure (CPAP).
After prolonged use of respiration apparatus, the systems of respiratory patients frequently become accustomed to this type of respiration and, accordingly, they cannot return to adequate natural breathing without the use of breathing apparatus. Accordingly, for purposes of withdrawal, the number of breathing cycles to which the patient is subjected must be reduced slowly until such time as he is capable of breathing spontaneously (IMV).
In a known respirator, respiratory gas is conducted in a line current through preparations, indicating and safety devices, as well as through a branch with an opening for the patient, and is then discharged into the atmosphere over a control valve. The delivery of the gas maintaining the respiration from the control valve is controlled by different pressures by means of a pneumatic control, connected to the control valve, so that corresponding selective inspiration and expiration states are provided in the opening leading to the patient.
The pneumatic control contains a variable pneumatic oscillator which repeatedly produces two pressure levels, varying with a time corresponding to the duration of the inspiration and expiration phase, as well as a bistable pneumatic logic element which is switched between its two stable states in response to the latter. In this way, the connected control chamber of the control valve is exposed alternately to two different gas pressures. By linking elements and logic elements, it is thus possible to obtain a plurality of operating methods or cycles, such as the IPPV, PEEP-CPAP and IMV respiration method. For the sake of brevity, these cycles or methods will be referred to by their respective initials as used hereinbefore.
A disadvantage of this prior art respirator, which works on a dynamic control principle, is high gas consumption. This is caused by a constant gas loss in the throttles through which the amount of gas taken from the gas supply as control gas flows into the atmosphere after it has performed its switching functions. A known apparatus according to this principle has a gas consumption of about 4 liters per minute, while normally 0.5 to 3 liters per minute of respiratory gases are required for patients treated with this apparatus. (See German Patent Disclosure DOS No. 2,525,359).